1. Field of the Invention
The present invention pertains to downhole well valves. More particularly, the present invention relates to techniques for selectively opening and closing wells at downhole locations.
2. Description of Prior Art
At various times during operations on wells, it is necessary to close the well completely, at least to upward flow of fluid. For example, during squeeze cementing operations a portion of the well is shut off to contain the cementing fluid. Where production must be interrupted, for example, a well under pressure must be plugged, or shut off at the surface.
Bridging plugs are known for use in shutting off wells at downhole locations. Such bridging plugs are lowered into the well, by wireline for example, and latched into place on a structure already in position in the well. When it is desired to open the well again, the bridging plug is retrieved by use of a fishing tool on a wireline, for example. Plugs may also be run in the well on a tubing string, and later retrieved by means of a tubing string. Such operations are time consuming and costly. Additionally, while the plug is being manipulated into or out of the well, the well is not closed, and pressure in the well must be maintained by a sufficient hydrostatic head.
Similarly, when it is necessary to round-trip a tubing string in order to accomplish varied operations in the well, the well must be maintained under sufficient hydrostatic head to prevent a blow-out. For example, if a well is to be tested and then cemented, it may be necessary to round trip the test string before cementing, or to maintain the test string in the well to hold the pressure while waiting on the cement.
It will be appreciated by those in the field that the operation of withdrawing the tubing string from a well and replacing same or another string is expensive. Further, such operations are inherently dangerous, as generally are all well-working operations involving insertion or withdrawal of tubing or other equipment, particularly in high pressure wells.
It is desirable to provide method and apparatus for selectively opening and closing a well at a downhole location without, for example, necessarily withdrawing a production string from the well for that purpose. Additionally, it is desirable to provide means whereby a well may be shut down against upward flow at a downhole location, and wherein a well may be quickly closed off at such a downhole location.